Prior Art
One of the well-known and most widespread types of hard finishing of gears is the generation grinding of the tooth flanks by means of a cylindrical grinding wheel profiled in a worm shape at its circumference, the so-called grinding worm. The gear, when being ground, is brought into meshing engagement with the grinding worm, the tooth flanks of the gear being ground by the grinding-worm thread flanks and the tooth root being ground by the tip part of the grinding worm thread. This means that, before the grinding of the gear, the grinding worm thread has to be completely profiled in accordance with the tooth-gap profile of the workpiece.
A whole series of methods is known for the profiling of the grinding worm thread, the most efficient and the most widespread being that in which one dressing profile disc each is used for the dressing of the left-hand flank and the right-hand flank and a forming roll is used for the dressing of the tip of the grinding worm thread. The three tools, which are combined to form a tool set and in which the outside dimensions of the forming roll have to correspond to the root radius and tooth height of the respective workpiece, permit a short dressing time, since all their active abrasive tool surfaces covered with hard-material grains are in use simultaneously during dressing. However, the advantage of the high efficiency of this dressing method is offset by the disadvantage of limited flexibility or a high setting-up cost.
In another method, by means of a rotating dressing tool coated with hard-material grains at the active circumference, the entire active profile of the grinding worm is profiled line by line in point contact, specifically in such a way that line is placed around line right next to each other until the entire active thread profile is dressed. This method requires only a single dressing tool and is exceptionally flexible with regard to the profile of the thread. However, it has the disadvantage of being very slow. This disadvantage partly still exists even if, as in DE-A 196 24 842 A1, the line-by-line profiling is combined with the use of dressing profile discs.